Multi-layer ceramic capacitor and method of producing the same

ABSTRACT

A multi-layer ceramic capacitor includes a first region, a second region, a multi-layer unit, and a side margin. In the first region, crystal grains including intragranular pores are dispersed. In the second region, crystal grains including intragranular pores are not dispersed. The multi-layer unit includes ceramic layers that are laminated in a first direction and include the second region, and internal electrodes disposed between the ceramic layers. The side margin covers the multi-layer unit from a second direction orthogonal to the first direction and includes a region, the region being adjacent to the multi-layer unit and including the first region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/647,566, filed Jan. 10, 2022; which is a continuation of U.S.application Ser. No. 16/395,618, filed Apr. 26, 2019, now U.S. Pat. No.11,257,624, issued Feb. 22, 2022; which claims the benefit of JapaneseApplication No. 2018-090320, filed May 9, 2018; which is herebyincorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a multi-layer ceramic capacitorincluding side margins provided in a later step, and to a method ofproducing the multi-layer ceramic capacitor.

Japanese Patent Application Laid-open Nos. 2016-001721 and 2017-028013each disclose a technique of providing side margins in a later step in amethod of producing a multi-layer ceramic capacitor, the side marginsprotecting the periphery of internal electrodes. In this technique, amulti-layer unit including internal electrodes, which are exposed onside surfaces of the multi-layer unit, is produced, and side margins areprovided to the side surfaces, thus providing a ceramic body.

However, in the technique of providing side margins in a later step, itis difficult to ensure reliability of moisture resistance or the like.Thus, the technique disclosed in each of Japanese Patent ApplicationLaid-open Nos. 2016-001721 and 2017-028013 achieves improvement insinterability of the side margins by adding silicon, as a sinteringadditive, to the side margins. Accordingly, the reliability of themulti-layer ceramic capacitor is improved.

SUMMARY

However, in the technique of adding silicon to the side margins, siliconcontained in the side margins is dispersed in the multi-layer unit atthe time of sintering, and an electrostatic capacitance of themulti-layer ceramic capacitor is likely to be lowered. Thus, thistechnique makes it difficult to provide a multi-layer ceramic capacitorhaving a large electrostatic capacitance.

In view of the circumstances as described above, it is desirable toprovide a multi-layer ceramic capacitor and a method of producing themulti-layer ceramic capacitor, which are capable of satisfying both of alarge electrostatic capacitance and high reliability.

According to an embodiment of the present disclosure, there is provideda multi-layer ceramic capacitor including a first region, a secondregion, a multi-layer unit, and a side margin.

In the first region, crystal grains including intragranular pores aredispersed.

In the second region, crystal grains including intragranular pores arenot dispersed.

The multi-layer unit includes ceramic layers that are laminated in afirst direction and include the second region, and internal electrodesdisposed between the ceramic layers.

The side margin covers the multi-layer unit from a second directionorthogonal to the first direction and includes a region, the regionbeing adjacent to the multi-layer unit and including the first region.

In the multi-layer ceramic capacitor, the first region is formed of ahydrothermal powder produced by a hydrothermal method. The hydrothermalpowder is a fine ceramic powder that can be produced at low cost and isformed of particles having a uniform particle size. In the first regionformed of the hydrothermal powder, a characteristic microstructure inwhich crystal grains including intragranular pores are dispersed isfound. In the first region, a large dielectric constant is difficult toobtain due to the existence of the intragranular pores.

In the present disclosure, in the side margin that does not contributeto the electrostatic capacitance, a region adjacent to at least themulti-layer unit is formed as the first region. Accordingly, anunsintered side margin including as a main component the hydrothermalpowder, which is a fine powder formed of particles having a uniformparticle size, comes into close contact with the side surface of themulti-layer unit along the side surface without gaps, and thus amulti-layer ceramic capacitor having high reliability is obtained.

Meanwhile, unlike the first region, the second region is free from thehydrothermal powder. The second region is formed of a ceramic powderproduced by a method different from the hydrothermal method, forexample, a method of obtaining a sufficiently large dielectric constant,such as a solid-phase method. Thus, in the second region, there is nomicrostructure in which crystal grains including intragranular pores aredispersed, and a large dielectric constant can be obtained.

In the present disclosure, the ceramic layers are formed as the secondregion. Accordingly, in the multi-layer ceramic capacitor, a largeelectrostatic capacitance can be obtained. In such a manner, in themulti-layer ceramic capacitor, the side margin and the ceramic layer areformed of different ceramic powders, so that both of a largeelectrostatic capacitance and high reliability can be satisfied.

The side margin may include the first region over the entire sidemargin.

In this configuration, in the side margin formed of the hydrothermalpowder, high sinterability is obtained over the entire side margin.Accordingly, the reliability of the multi-layer ceramic capacitor isfurther improved.

The side margin may include an external layer including the secondregion, and a connection layer that is disposed between the externallayer and the multi-layer unit and includes the first region.

In this configuration, the multi-layer unit and the external layer aresuitably bonded to each other via an unsintered connection layer formedof the hydrothermal powder.

The first region may include silicon of 0.5 mol % or less.

In the multi-layer ceramic capacitor, reduction in electrostaticcapacitance due to the dispersion of silicon from the side margin to themulti-layer unit is less likely to be caused.

The side margin may have a grain boundary pore rate of 5% or less.

In this configuration, the reliability of the multi-layer ceramiccapacitor is further improved.

Each of the first region and the second region may include polycrystalhaving a Perovskite structure including barium and titanium.

According to another embodiment of the present disclosure, there isprovided a method of producing a multi-layer ceramic capacitor, themethod including: preparing a first powder including, as a maincomponent, ceramic particles having a Perovskite structure having anaxis ratio c/a of 1.008 or less and including intragranular pores;preparing a second powder including, as a main component, ceramicparticles free from intragranular pores; producing an unsinteredmulti-layer unit that includes ceramic layers laminated in a firstdirection and including the second powder as a main component, andinternal electrodes disposed between the ceramic layers; producing aceramic body by forming a side margin including the first powder as amain component on a side surface of the multi-layer unit, the sidesurface facing in a second direction orthogonal to the first direction;and sintering the ceramic body.

The side margin may be formed by attaching a ceramic sheet including thefirst powder as a main component to the side surface.

The ceramic sheet may be free from silicon.

Further, according to another embodiment of the present disclosure,there is provided a method of producing a multi-layer ceramic capacitor,the method including: preparing a first powder including, as a maincomponent, ceramic particles having a Perovskite structure having anaxis ratio c/a of 1.008 or less and including intragranular pores;preparing a second powder including, as a main component, ceramicparticles free from intragranular pores; producing an unsinteredmulti-layer unit that includes ceramic layers laminated in a firstdirection and including the second powder as a main component, andinternal electrodes disposed between the ceramic layers; producing aceramic body by attaching a ceramic sheet to a side surface of themulti-layer unit via a connection layer including the first powder as amain component, the side surface facing in a second direction orthogonalto the first direction; and sintering the ceramic body.

The connection layer may be free from silicon.

In those methods, the first powder is produced by the hydrothermalmethod. This allows the multi-layer ceramic capacitor to be produced. Inparticular, the first powder that is the hydrothermal powder has a lowaxis ratio c/a, that is, low crystallinity. Thus, in the side marginformed of the first powder, high sinterability is obtained. Accordingly,the reliability of the multi-layer ceramic capacitor is furtherimproved.

The first powder may have a mean particle size of 5 nm or more and 500nm or less.

The second powder may be produced by a solid-phase method.

As described above, according to the present disclosure, it is possibleto provide a multi-layer ceramic capacitor and a method of producing themulti-layer ceramic capacitor, which are capable of satisfying both of alarge electrostatic capacitance and high reliability.

These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of embodiments thereof, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a multi-layer ceramic capacitoraccording to a first embodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the multi-layer ceramic capacitortaken along the A-A′ line in FIG. 1 ;

FIG. 3 is a cross-sectional view of the multi-layer ceramic capacitortaken along the B-B′ line in FIG. 1 ;

FIG. 4 is a partial cross-sectional enlarged view of FIG. 3 ;

FIG. 5 is a flowchart showing a method of producing the multi-layerceramic capacitor;

FIGS. 6A, 6B, and 6C are each a plan view showing a production processof the multi-layer ceramic capacitor;

FIG. 7 is a perspective view showing the production process of themulti-layer ceramic capacitor;

FIG. 8 is a plan view showing the production process of the multi-layerceramic capacitor;

FIG. 9 is a perspective view showing the production process of themulti-layer ceramic capacitor;

FIG. 10 is a perspective view showing the production process of themulti-layer ceramic capacitor;

FIG. 11 is a cross-sectional view of a multi-layer ceramic capacitoraccording to a second embodiment of the present disclosure;

FIG. 12 is a partial cross-sectional enlarged view of FIG. 11 ; and

FIG. 13 is a schematic view showing a production process of themulti-layer ceramic capacitor.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings.

In the figures, an X axis, a Y axis, and a Z axis orthogonal to oneanother are shown as appropriate. The X axis, the Y axis, and the Z axisare common in all figures.

I First Embodiment 1. Overall Configuration of Multi-layer CeramicCapacitor 10

FIGS. 1 to 3 each show a multi-layer ceramic capacitor 10 according to afirst embodiment of the present disclosure. FIG. 1 is a perspective viewof the multi-layer ceramic capacitor 10. FIG. 2 is a cross-sectionalview of the multi-layer ceramic capacitor 10 taken along the A-A′ linein FIG. 1 . FIG. 3 is a cross-sectional view of the multi-layer ceramiccapacitor 10 taken along the B-B′ line in FIG. 1 .

The multi-layer ceramic capacitor 10 includes a ceramic body 11, a firstexternal electrode 14, and a second external electrode 15. Typically,the ceramic body 11 has two end surfaces facing in the X-axis direction,two side surfaces facing in the Y-axis direction, and two main surfacesfacing in the Z-axis direction. Ridges connecting the respectivesurfaces of the ceramic body 11 are chamfered.

It should be noted that the shape of the ceramic body 11 is not limitedto the shape as described above. In other words, the ceramic body 11does not need to have a rectangular parallelepiped shape as shown inFIGS. 1 to 3 . For example, the surfaces of the ceramic body 11 may becurved surfaces, and the ceramic body 11 may be rounded as a whole.

The first external electrode 14 and the second external electrode 15cover both the end surfaces of the ceramic body 11 that face in theX-axis direction, and extend to four surfaces (two main surfaces and twoside surfaces) that are connected to both the end surfaces facing in theX-axis direction. With this configuration, both of the first externalelectrode 14 and the second external electrode 15 have U-shaped crosssections parallel to the X-Z plane and the X-Y plane.

The ceramic body 11 includes a multi-layer unit 16 and side margins 17.The side margins 17 cover the entire areas of both the side surfaces ofthe multi-layer unit 16 that face in the Y-axis direction. Themulti-layer unit 16 includes a capacitance forming unit 18 and covers19. The covers 19 cover the upper and lower surfaces of the capacitanceforming unit 18 in the Z-axis direction.

The capacitance forming unit 18 includes a plurality of ceramic layers20, a plurality of first internal electrodes 12, and a plurality ofsecond internal electrodes 13. The plurality of ceramic layers 20 areflat plate-like ceramic layers extending parallel to the X-Y plane andlaminated in the Z-axis direction. The covers 19 do not include thefirst and second internal electrodes 12 and 13.

The first and second internal electrodes 12 and 13 are alternatelydisposed in the Z-axis direction between the plurality of ceramic layers20. The first internal electrodes 12 are connected to the first externalelectrode 14 and are apart from the second external electrode 15. Thesecond internal electrodes 13 are connected to the second externalelectrode 15 and are apart from the first external electrode 14.

In such a manner, in the ceramic body 11, except for both the endsurfaces facing in the X-axis direction, to which the first externalelectrode 14 and the second external electrode 15 are provided, surfacesof the capacitance forming unit 18 are covered with the side margins 17and the covers 19. The side margins 17 and the covers 19 have mainfunctions of protecting the periphery of the capacitance forming unit 18and ensuring insulation properties of the first and second internalelectrodes 12 and 13.

The first and second internal electrodes 12 and 13 are each formed of anelectrically conductive material and function as internal electrodes ofthe multi-layer ceramic capacitor 10. Examples of the electricallyconductive material include a metal material containing nickel (Ni),copper (Cu), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), oran alloy of them.

A region other than the first and second internal electrodes 12 and 13in the capacitance forming unit 18 is formed of dielectric ceramics. Inthe multi-layer ceramic capacitor 10, in order to increase capacitancesof the ceramic layers 20 provided between the first internal electrodes12 and the second internal electrodes 13, dielectric ceramics having ahigh dielectric constant is used as dielectric ceramics forming thecapacitance forming unit 18.

More specifically, in the multi-layer ceramic capacitor 10, polycrystalof a barium titanate (BaTiO₃) based material, i.e., polycrystal having aPerovskite structure containing barium (Ba) and titanium (Ti) is used asthe dielectric ceramics having a high dielectric constant that forms thecapacitance forming unit 18. This provides a large capacitance to themulti-layer ceramic capacitor 10.

It should be noted that the capacitance forming unit 18 may have acomposition system of strontium titanate (SrTiO₃), calcium titanate(CaTiO₃), magnesium titanate (MgTiO₃), calcium zirconate (CaZrO₃),calcium zirconate titanate (Ca(Zr,Ti)O₃), barium zirconate (BaZrO₃),titanium oxide (TiO₂), or the like.

The side margins 17 and the covers 19 are also formed of dielectricceramics. The material forming the side margins 17 and the covers 19 maybe insulating ceramics. If dielectric ceramics having a compositionsystem similar to that of the ceramic layers 20 of the capacitanceforming unit 18 is used, internal stress in the ceramic body 11 issuppressed.

With the configuration described above, when a voltage is appliedbetween the first external electrode 14 and the second externalelectrode 15 in the multi-layer ceramic capacitor 10, the voltage isapplied to the plurality of ceramic layers 20 between the first internalelectrodes 12 and the second internal electrodes 13. Accordingly, themulti-layer ceramic capacitor 10 stores charge corresponding to thevoltage applied between the first external electrode 14 and the secondexternal electrode 15.

It should be noted that the configuration of the multi-layer ceramiccapacitor 10 according to this embodiment is not limited to theconfiguration shown in FIGS. 1 to 3 and can be changed as appropriate.For example, the number of first internal electrodes 12 and secondinternal electrodes 13 and the thickness of the ceramic layer 20 can bedetermined as appropriate according to the size and performance expectedfor the multi-layer ceramic capacitor 10.

2. Detailed Configuration of Ceramic Body 11

FIG. 4 is a partial cross-sectional view of the ceramic body 11, showingthe vicinity of the boundary between the side margin 17 and thecapacitance forming unit 18 in FIG. 3 in an enlarged manner. FIG. 4schematically shows a microstructure of the ceramic body 11. In theceramic body 11, the side margin 17 and the ceramic layers 20 of thecapacitance forming unit 18 are each formed as polycrystal.

More specifically, as shown in FIG. 4 , the ceramic body 11 has acharacteristic microstructure in which crystal grains includingintragranular pores P exist. The intragranular pore P is formed as aminute void within the crystal grain. In other words, the intragranularpore P is distinguished from a grain boundary pore, which is generallyconsidered as a void formed at a grain boundary between adjacent crystalgrains.

The crystal grains including the intragranular pores P are not presentin the entire region of the ceramic body 11. Specifically, in theceramic body 11, the side margin 17 is formed as a first region in whichthe crystal grains including the intragranular pores P are dispersed,and the ceramic layers 20 of the capacitance forming unit 18 are formedas a second region in which the crystal grains including theintragranular pores P are not dispersed.

Although details will be described later, the side margin 17 is formedof a hydrothermal powder, which is a ceramic powder produced by ahydrothermal method. The hydrothermal powder has a characteristic ofincluding, as a main component, ceramic particles includingintragranular pores P within the crystal grains. Thus, in the sidemargin 17, many crystal grains including the intragranular pores Presulting from the hydrothermal powder are left after sintering.

The fact that the raw material is the hydrothermal powder can beconfirmed by the dispersion of the crystal grains including theintragranular pores P. In other words, in the side margin 17 formed ofthe hydrothermal powder, the crystal grains including the intragranularpores P are dispersed in the entire side margin 17. It should be notedthat all of the crystal grains do not need to include the intragranularpores P in the side margin 17.

The amount of the crystal grains including the intragranular pores P canbe evaluated by an abundance rate of the intragranular pores, which is aproportion of the crystal grains including the intragranular pores P outof the crystal grains. If the raw material is the hydrothermal powder,the abundance rate of the intragranular pores is 1% or more. In otherwords, the abundance rate of the intragranular pores in the side margin17 formed of the hydrothermal powder is 1% or more.

For example, the abundance rate of the intragranular pores can beobtained as a proportion of the crystal grains including theintragranular pores P out of all the crystal grains observed in apredetermined region in an image of a cross section of the side margin17, the image being captured with a scanning electron microscope at amagnification of 5 million times. At that time, for example, a voidwhose size is 5 nm or more, which is observed within a crystal grain,can be set as the intragranular pore P.

In the dielectric ceramics formed of the hydrothermal powder, a highdielectric constant is difficult to obtain because of the existence ofthe intragranular pores P that are voids. However, in the side margin 17that does not contribute to an electrostatic capacitance, a highdielectric constant is not required. In other words, even if the sidemargin 17 is formed of the hydrothermal powder, the electrostaticcapacitance of the multi-layer ceramic capacitor 10 is not impaired.

Meanwhile, if the ceramic layers 20 of the capacitance forming unit 18are formed of the hydrothermal powder, the electrostatic capacitance ofthe multi-layer ceramic capacitor 10 is reduced. Thus, the hydrothermalpowder is not used to form the ceramic layers 20. As a result, theceramic layers 20 become polycrystal formed of crystal grains free fromintragranular pores P.

Although details will be described later, the ceramic layer 20 is formedof a ceramic powder formed by a method capable of obtaining asufficiently large dielectric constant, such as a solid-phase method,unlike the hydrothermal method. Thus, a large electrostatic capacitanceis obtained in the ceramic layer 20. It should be noted that the ceramiclayer 20 may incidentally include a few crystal grains including theintragranular pores P. Specifically, the abundance rate of theintragranular pores in the ceramic layer 20 is 0.001% or less.

The intragranular pores P in the side margin 17 are each included in thecrystal grain and thus less likely to be an entry pathway for moisture.Thus, even if the side margin 17 is formed of the hydrothermal powder,the moisture resistance of the multi-layer ceramic capacitor 10 is lesslikely to be impaired. From a similar perspective, it is favorable thatthe number of grain boundary pores formed at grain boundaries betweenthe crystal grains is small in the side margin 17.

It is favorable that the side margin 17 has a grain boundary pore rateof 5% or more. The grain boundary pore rate is a proportion of the grainboundary pores (excluding intragranular pores P) in the cross sectionthereof. For example, the grain boundary pore rate can be calculated asa proportion of an area occupied by the grain boundary pores in apredetermined region of an image of the cross section of the side margin17, the image being captured with a scanning electron microscope at amagnification of 5 million times.

Further, although detailed will be described later, since thehydrothermal powder has high sinterability, the side margin 17 canobtain high sinterability without including silicon as a sinteringadditive. This can inhibit the electrostatic capacitance from beingreduced due to dispersion of silicon from the side margin 17 to theceramic layers 20 of the capacitance forming unit 18 at the time ofsintering.

It should be noted that in the ceramic body 11 the cover 19 is typicallyformed as the second region that is not formed of the hydrothermalpowder, like the ceramic layers 20. However, the cover 19 does notcontribute to the electrostatic capacitance just like the side margins17, and thus may be formed as the first region formed of thehydrothermal powder.

3. Method of Producing Multi-layer Ceramic Capacitor 10

FIG. 5 is a flowchart showing a method of producing the multi-layerceramic capacitor 10. FIGS. 6A to 10 are views each showing a productionprocess of the multi-layer ceramic capacitor 10. Hereinafter, the methodof producing the multi-layer ceramic capacitor 10 will be describedaccording to FIG. 5 with reference to FIGS. 6A to 10 as appropriate.

3.1 Step S01: Preparation of First Powder

In Step S01, a first powder that is a ceramic powder for forming theside margins 17 is prepared. In other words, the first powder is ahydrothermal powder produced by a hydrothermal method. For example, thehydrothermal powder of barium titanate is obtained when titanium oxideand barium hydroxide are synthesized in a pressure vessel containing hotwater by a hydrothermal method.

Since the hydrothermal method allows the ceramic powder to be producedat low cost, using the hydrothermal powder to form the side margins 17can lead to reduction in manufacturing cost of the multi-layer ceramiccapacitor 10. Further, the hydrothermal powder is obtained as a finepowder formed of substantially spherical particles having a uniformparticle size and, for example, has a mean particle size of 5 nm or moreand 500 nm or less.

Furthermore, the hydrothermal method is likely to cause various latticedefects, that is, reduce the crystallinity of the hydrothermal powder.In this embodiment, the sinterability of the side margins 17 can beimproved by purposefully using the hydrothermal powder having lowcrystallinity. The action of the hydrothermal powder will be describedin detail in the section of Step S07 (Sintering).

The crystallinity of the Perovskite structure can be evaluated by anaxis ratio c/a, which is a ratio of the length of a c-axis to the lengthof an a-axis in a unit lattice. In an ideal crystalline structure, theaxis ratio c/a is approximately 1.01. In the hydrothermal powder, theaxis ratio c/a is 1.008 or less. The axis ratio c/a can be calculatedfrom a spectrum obtained in X-ray diffraction, for example.

3.2 Step S02: Preparation of Second Powder

In Step S02, a second powder that is a ceramic powder for forming theceramic layers 20 is prepared. The second powder is a solid-phase powderproduced by a method other than the hydrothermal method, and in thisembodiment, produced by a solid-phase method. For example, thesolid-phase powder of barium titanate is obtained when a mixed powder oftitanium oxide and barium carbonate is heated to cause a solid-phasereaction.

3.3 Step S03: Preparation of Ceramic Sheet

In Step S03, first ceramic sheets 101 and second ceramic sheets 102 forforming the capacitance forming unit 18, third ceramic sheets 103 forforming the covers 19, and fourth ceramic sheets 117 for forming theside margins 17 are prepared.

The first, second, third, and fourth ceramic sheets 101, 102, 103, and117 include a ceramic powder as a main component and are formed asunsintered dielectric green sheets that are formed into sheets by usinga solvent and a binder. For the formation of the first, second, third,and fourth ceramic sheets 101, 102, 103, and 117, a roll coater or adoctor blade can be used, for example.

More specifically, the first, second, and third ceramic sheets 101, 102,and 103 are formed using the second powder, as a main component, whichis the solid-phase powder prepared in Step S02. Meanwhile, the fourthceramic sheets 117 forming the side margins 17 are formed using thefirst powder, as a main component, which is the hydrothermal powderprepared in Step S01.

As described above, the hydrothermal powder is a fine powder formed ofsubstantially spherical particles having a uniform particle size. Thus,the hydrothermal powder is likely to be dispersed in a solvent. Further,slurry of the hydrothermal powder dispersed in the solvent and thebinder is flexibly deformable and thus has high formability. Thus,high-quality fourth ceramic sheets 117 are obtained by using thehydrothermal powder.

Further, in general, high sinterability is likely to be obtained in themulti-layer unit 16 including the first and second internal electrodes12 and 13 having a low sintering temperature, whereas high sinterabilityis less likely to be obtained in the side margins 17. Thus, a largeamount of sintering additive is generally added to the ceramic sheetsfor forming the side margins 17.

In this regard, it is unnecessary to add a large amount of sinteringadditive to the fourth ceramic sheets 117 including as a main componentthe hydrothermal powder having high sinterability. In particular, it isfavorable that silicon is not added to the fourth ceramic sheets 117because silicon is likely to cause reduction in electrostaticcapacitance due to the dispersion thereof to the ceramic layers 20 ofthe capacitance forming unit 18 at the time of sintering.

It should be noted that the third ceramic sheets 103 for forming thecovers 19 may be formed of the first powder, as a main component, whichis prepared in Step S01, like the fourth ceramic sheets 117. Using theinexpensive hydrothermal powder for the third ceramic sheets 103 canalso lead to further reduction in manufacturing cost of the multi-layerceramic capacitor 10.

FIGS. 6A, 6B, and 6C are plan views of the first, second, and thirdceramic sheets 101, 102, and 103, respectively. At this stage, thefirst, second, and third ceramic sheets 101, 102, and 103 are eachformed as a large-sized sheet that is not singulated. FIGS. 6A, 6B, and6C each show cutting lines Lx and Ly used when the sheets are singulatedinto the multi-layer ceramic capacitors 10. The cutting lines Lx areparallel to the X axis, and the cutting lines Ly are parallel to the Yaxis.

As shown in FIGS. 6A, 6B, and 6C, unsintered first internal electrodes112 corresponding to the first internal electrodes 12 are formed on thefirst ceramic sheet 101, and unsintered second internal electrodes 113corresponding to the second internal electrodes 13 are formed on thesecond ceramic sheet 102. It should be noted that no internal electrodesare formed on the third ceramic sheet 103 corresponding to the cover 19.

The first internal electrodes 112 and the second internal electrodes 113can be formed by applying an optional electrically conductive paste tothe first ceramic sheets 101 and the second ceramic sheets 102,respectively. A method of applying the electrically conductive paste canbe optionally selected from well-known techniques. For example, for theapplication of the electrically conductive paste, a screen printingmethod or a gravure printing method can be used.

In the first and second internal electrodes 112 and 113, gaps aredisposed in the X-axis direction along the cutting lines Ly for everyother cutting line Ly. The gaps of the first internal electrodes 112 andthe gaps of the second internal electrodes 113 are alternately disposedin the X-axis direction. In other words, a cutting line Ly passingthrough a gap between the first internal electrodes 112 and a cuttingline Ly passing through a gap between the second internal electrodes 113are alternately disposed.

3.4 Step S04: Lamination

In Step S04, the first, second, and third ceramic sheets 101, 102, and103 prepared in Step S03 are laminated as shown in FIG. 7 , to produce amulti-layer sheet 104. In the multi-layer sheet 104, the first ceramicsheets 101 and the second ceramic sheets 102 that correspond to thecapacitance forming unit 18 are alternately laminated in the Z-axisdirection.

Further, in the multi-layer sheet 104, the third ceramic sheets 103corresponding to the covers 19 are laminated on the uppermost andlowermost surfaces of the first and second ceramic sheets 101 and 102alternately laminated in the Z-axis direction. It should be noted thatin the example shown in FIG. 7 , three third ceramic sheets 103 arelaminated on each of the uppermost and lowermost surfaces of thelaminated first and second ceramic sheets 101 and 102, but the number ofthird ceramic sheets 103 can be changed as appropriate.

The multi-layer sheet 104 is integrated by pressure-bonding the first,second, and third ceramic sheets 101, 102, and 103. For thepressure-bonding of the first, second, and third ceramic sheets 101,102, and 103, for example, hydrostatic pressing or uniaxial pressing isfavorably used. This makes it possible to obtain a high-densitymulti-layer sheet 104.

3.5 Step S05: Cutting

In Step S05, the multi-layer sheet 104 obtained in Step S04 is cut alongthe cutting lines Lx and Ly as shown in FIG. 8 , to produce anunsintered multi-layer unit 116. The multi-layer unit 116 corresponds tothe multi-layer unit 16 obtained after sintering. For cutting of themulti-layer sheet 104, for example, a rotary blade or a push-cuttingblade can be used.

More specifically, the multi-layer sheet 104 is cut along the cuttinglines Lx and Ly while being held by a holding member C. Thus, themulti-layer sheet 104 is singulated, and the multi-layer units 116 areobtained. At that time, the holding member C is not cut, and thus themulti-layer units 116 are connected via the holding member C.

FIG. 9 is a perspective view of the multi-layer unit 116 obtained inStep S05. The multi-layer unit 116 includes a capacitance forming unit118 and covers 119. In the multi-layer unit 116, the first and secondinternal electrodes 112 and 113 are exposed on the cut surfaces, i.e.,both the side surfaces facing in the Y-axis direction. Ceramic layers120 are formed between the first and second internal electrodes 112 and113.

3.6 Step S06: Formation of Side Margin

In Step S06, the fourth ceramic sheets 117 prepared in Step S03 areattached to the multi-layer unit 116 obtained in Step S05, and anunsintered ceramic body 111 is thus produced. In other words, the fourthceramic sheets 117 are formed as unsintered side margins 17.

In Step S06, the fourth ceramic sheets 117 are attached to both the sidesurfaces that are the cut surfaces of the multi-layer unit 116 obtainedin Step S05 and face in the Y-axis direction. Thus, in Step S06, it isfavorable to detach the multi-layer unit 116 from the holding member Cin advance and rotate the multi-layer unit 116 by 90 degrees.

FIG. 10 is a perspective view of the unsintered ceramic body 111obtained in Step S06. In Step S06, for example, the fourth ceramicsheets 117, each of which is cut to fit the outer shape of the sidesurface of the multi-layer unit 116, can be attached to both the sidesurfaces of the multi-layer unit 116. Accordingly, the unsinteredceramic body 111 shown in FIG. 10 is obtained.

The fourth ceramic sheet 117 including as a main component thehydrothermal powder, which is a fine powder formed of particles having auniform particle size, is flexibly deformable while following the minuteirregularities of the side surface of the multi-layer unit 116, and cancome into close contact with the side surface of the multi-layer unit116 along with the side surface. Thus, in the ceramic body 111, a gap isless likely to be generated between the fourth ceramic sheet 117 and themulti-layer unit 116.

It should be noted that the method of forming the unsintered side margin17 is not limited to the method described above. For example, the fourthceramic sheet 117 may be cut to fit the outline of the side surface ofthe multi-layer unit 116 after being attached to the side surface of themulti-layer unit 116. Furthermore, the fourth ceramic sheet 117 may bepunched out by the side surface of the multi-layer unit 116.

3.7 Step S07: Sintering

In Step S07, the unsintered body 111 obtained in Step S06 is sintered toproduce the ceramic body 11 of the multi-layer ceramic capacitor 10shown in FIGS. 1 to 3 . In other words, in Step S07, the multi-layerunit 116 becomes the multi-layer unit 16, and the fourth ceramic sheets117 become the side margins 17.

A sintering temperature in Step S07 can be determined on the basis of asintering temperature for the ceramic body 111. For example, when abarium titanate based material is used as dielectric ceramics, thesintering temperature can be set to approximately 1,000 to 1,300° C.Further, sintering can be performed in a reduction atmosphere or alow-oxygen partial pressure atmosphere, for example.

In the hydrothermal powder having low crystallinity, the movement ofsubstances is likely to occur at the time of sintering because ofrearrangement of atoms forming respective ceramic particles. Further, inthe hydrothermal powder including the intragranular pores P, a surfacearea is increased by a portion corresponding to the intragranular poresP. Accordingly, in the hydrothermal powder, a diffusion pathway forsubstances at the sintering is increased, and thus the movement ofsubstances is more likely to occur.

Therefore, in the fourth ceramic sheets 117, the movement of substancesin the hydrothermal powder starts at a relatively low temperature, andsintering progresses. In the fourth ceramic sheets 117, the movement ofsubstances actively occurs in the course of sintering, and thussintering is accelerated. Accordingly, the side margins 17 having highsinterability and a few grain boundary pores are obtained.

In such a manner, in this embodiment, the side margins 17 having highsinterability are obtained without using silicon as a sinteringadditive. Thus, in the multi-layer ceramic capacitor 10, reduction inelectrostatic capacitance due to the dispersion of silicon from the sidemargins 17 to the ceramic layers 20 of the capacitance forming unit 18can be inhibited from occurring.

Further, in the multi-layer ceramic capacitor 10, reduction inmechanical strength of the side margins 17 due to segregation of hyalinecontaining silicon at the grain boundaries between crystal grainsforming the side margins 17 is less likely to occur. Thus, in themulti-layer ceramic capacitor 10, generation of cracks due to anexternal force such as thermal shock is inhibited.

Furthermore, as described above, since the multi-layer unit 116 and thefourth ceramic sheet 117 are in close contact with each other withoutgaps, gaps are difficult to occur between the multi-layer unit 16 andthe side margin 17 in the ceramic body 11 obtained after sintering.Accordingly, higher moisture resistance is obtained in the multi-layerceramic capacitor 10.

It should be noted that in the configuration in which silicon is notadded to the fourth ceramic sheets 117, the side margins 17 containingno silicon are typically obtained. Given that a small amount of siliconcontained in the capacitance forming unit 118 is dispersed to the fourthceramic sheets 117, the content of silicon in the side margin 17 is keptequal to or less than 0.5 mol %.

3.8 Step S08: Formation of External Electrode

In Step S08, the first external electrode 14 and the second externalelectrode 15 are formed on the ceramic body 11 obtained in Step S07, toproduce the multi-layer ceramic capacitor 10 shown in FIGS. 1 to 3 . InStep S08, for example, base films, intermediate films, and surface filmsforming the first and second external electrodes 14 and 15 are formed onthe end surfaces of the ceramic body 11 that face in the X-axisdirection.

More specifically, in Step S08, first, an unsintered electrode materialis applied so as to cover both the end surfaces of the ceramic body 11that face in the X-axis direction. The applied unsintered electrodematerials are subjected to baking in a reduction atmosphere or alow-oxygen partial pressure atmosphere, for example, to form base filmsof the first and second external electrodes 14 and 15 on the ceramicbody 11.

On the base films of the first and second external electrodes 14 and 15,which are baked onto the ceramic body 11, intermediate films of thefirst and second external electrodes 14 and 15 are then formed, andsurface films of the first and second external electrodes 14 and 15 arefurther formed. For the formation of the intermediate films and thesurface films of the first and second external electrodes 14 and 15, forexample, plating such as electrolytic plating can be used.

It should be noted that part of the processing in Step S08 may beperformed before Step S07. For example, before Step S07, the unsinteredelectrode material may be applied to both the end surfaces of theunsintered ceramic body 111 that face in the X-axis direction.Accordingly, in Step S07, sintering of the unsintered ceramic body 111and baking of the unsintered electrode material can be simultaneouslyperformed.

4. Examples

Hereinafter, Example of the embodiment described above will bedescribed. The configuration of Example is merely an example of theconfiguration included in this embodiment. In Example, the multi-layerceramic capacitor 10 was produced by using the production methoddescribed above. Specifically, a hydrothermal powder of barium titanatehaving an axis ratio c/a of 0.996 was used to form the side margins 17without adding silicon thereto.

In contrast, a multi-layer ceramic capacitor according to Comparativeexample, which is different from that of this embodiment in theconfiguration of the side margin, was produced. In Comparative example,a solid-phase powder of barium titanate having an axis ratio c/a of 1.01was used to form the side margins 17 by adding 1 mol % of siliconthereto. In Example and Comparative example, the configurations thereofare similar to each other except for the raw material of the sidemargin.

An electrostatic capacitance measurement, a heat resistance test, and amoisture resistance test were performed for samples according to Exampleand Comparative example. In the heat resistance test, the samplesaccording to Example and Comparative example were heated to atemperature of 350° C. in a reflow oven. In the moisture resistancetest, the samples according to Example and Comparative example were heldfor 1,000 hours at a temperature of 45° C. and a humidity of 95% underapplication of a rated voltage of 10 V.

The heat resistance test and the moisture resistance test were performedon 1000 samples according to each of Example and Comparative example. Inthe heat resistance test, samples in which cracks were generated weredetermined as defectives in heat resistance. In the moisture resistancetest, samples whose electric resistance value was smaller than 10 MSΩwere determined as defectives in moisture resistance. Table 1 showsresults of those evaluations.

TABLE 1 Number of Number of Electrostatic defectives in defectives incapacitance heat resistance moisture resistance Example 22.1 μF 0/10000/1000 Comparative 20.3 μF 3/1000 5/1000 example

As shown in Table 1, in the samples according to Example, a largerelectrostatic capacitance was obtained than that in the samplesaccording to Comparative example. Since silicon is added to the sidemargin in the samples according to Comparative example, it is consideredthat the electrostatic capacitance is reduced due to the dispersion ofsilicon from the side margin to the ceramic layer at the time ofsintering.

Further, the defectives in heat resistance were not generated in thesamples according to Example, whereas the defectives in heat resistancewere generated in the samples according to Comparative example. In thesamples according to Comparative example, it is considered that cracksare likely to be generated due to thermal shock because of segregationof hyaline containing silicon at grain boundaries between crystal grainsin the side margin.

Furthermore, the defectives in moisture resistance were not generated inthe samples according to Example, whereas the defectives in moistureresistance were generated in the samples according to Comparativeexample. In the samples according to Comparative example, it isconsidered that the moisture resistance is impaired by a gap generatedbetween the side margin and the multi-layer unit, the influence of agrain boundary pore of the side margin, or the like.

II Second Embodiment

FIG. 11 is a cross-sectional view of a multi-layer ceramic capacitor 210according to a second embodiment of the present disclosure. Themulti-layer ceramic capacitor 210 includes side margins 217. In themulti-layer ceramic capacitor 210, the configuration of the side margin217 is different from that of the first embodiment, and the otherconfigurations are common to those of the first embodiment.

The side margin 217 has a multi-layer structure in a thickness direction(Y-axis direction) and includes an external layer 217 a and a connectionlayer 217 b. The external layer 217 a is disposed on the outer side inthe Y-axis direction and forms the side surface of a ceramic body 211.The connection layer 217 b is disposed between the multi-layer unit 16and the external layer 217 a and connects the external layer 217 a tothe side surface of the multi-layer unit 16.

FIG. 12 is a partial cross-sectional view of the ceramic body 211,showing the vicinity of the boundary between the side margin 217 and thecapacitance forming unit 18 in FIG. 11 in an enlarged manner. In theside margin 217, the connection layer 217 b is formed as a first regionformed of the hydrothermal powder, and the external layer 217 a isformed as a second region that is not formed of the hydrothermal powder.

Therefore, in the side margin 217, the crystal grains including theintragranular pores P are dispersed in the connection layer 217 b, andthe crystal grains including the intragranular pores P are not dispersedin the external layer 217 a. It should be noted that, in the side margin217, the connection layer 217 b only needs to be disposed in a regionadjacent to the multi-layer unit 16, and a layer other than the externallayer 217 a and the connection layer 217 b may be included.

The ceramic body 211 having the configuration descried above is obtainedby sintering an unsintered ceramic body 311 shown in FIG. 13 . In theceramic body 311, a fifth ceramic sheet 317 a forming the external layer217 a is disposed on each side surface of the multi-layer unit 116 via asixth ceramic sheet 317 b forming the connection layer 217 b.

The fifth ceramic sheet 317 a forming the external layer 217 a is formedusing the second powder, as a main component, which is the solid-phasepowder. The sixth ceramic sheet 317 b forming the connection layer 217 bis formed using the first powder, as a main component, which is thehydrothermal powder. Subsequently, the fifth ceramic sheet 317 a and thesixth ceramic sheet 317 b are attached to the side surface of themulti-layer unit 116.

The sixth ceramic sheet 317 b including the hydrothermal powder, as amain component, which is a fine powder formed of particles having auniform particle size, is flexibly deformable while following the shapesof the side surface of the multi-layer unit 116 and the fifth ceramicsheet 317 a. Accordingly, the sixth ceramic sheet 317 b can come intoclose contact with both of the multi-layer unit 116 and the fifthceramic sheet 317 a.

Thus, in the ceramic body 211 obtained by sintering the ceramic body311, a gap is less likely to be generated between the multi-layer unit116 and the side margin 217. Further, in the connection layer 217 b ofthe side margin 217 formed by the hydrothermal method, highsinterability is obtained. Therefore, in the multi-layer ceramiccapacitor 210, high moisture resistance is obtained.

It should be noted that in the side margin 217 of the multi-layerceramic capacitor 210, the external layer 217 a may also be formed asthe first region formed of the hydrothermal powder as in the case of theconnection layer 217 b. In this case, the fifth ceramic sheet 317 aforming the external layer 217 a can be formed using the first powder,which is the hydrothermal powder, as a main component.

III Other Embodiments

While the embodiments of the present disclosure have been describedhereinabove, the present disclosure is not limited to the embodimentsdescribed above, and it should be appreciated that the presentdisclosure may be variously modified.

For example, in the multi-layer ceramic capacitor, the capacitanceforming unit may be divided into capacitance forming units in the Z-axisdirection. In this case, in each capacitance forming unit, the firstinternal electrodes and the second internal electrodes only need to bealternately disposed along the Z-axis direction. In a portion where thecapacitance forming units are next to each other, the first internalelectrodes or the second internal electrodes may be continuouslydisposed.

Further, the method of forming the side margin is not limited to themethod of using the ceramic sheet. For example, a dip method ofimmersing the side surfaces of the multi-layer unit into ceramic slurryincluding as a main component the hydrothermal powder may be used. Evenin the side margin formed by such a method, high sinterability isobtained as in the case of the method described above.

What is claimed is:
 1. A multi-layer ceramic capacitor, comprising: afirst region in which crystal grains including intragranular pores aredispersed; a second region in which crystal grains includingintragranular pores are not dispersed; a multi-layer unit including acapacitance forming unit including ceramic layers that are laminated ina first direction and include the second region, and internal electrodesdisposed between the ceramic layers; and a cover that covers thecapacitance forming unit from the first direction and includes a region,the region being adjacent to the capacitance forming unit and includingthe first region over the entire cover, and a side margin that coversthe multi-layer unit from a second direction orthogonal to the firstdirection, wherein an abundance rate of the intragranular pores in thefirst region is 1% or more.
 2. The multi-layer ceramic capacitoraccording to claim 1, wherein the first region includes silicon of 0.5mol % or less.
 3. The multi-layer ceramic capacitor according to claim1, wherein the cover has a grain boundary pore rate of 5% or less. 4.The multi-layer ceramic capacitor according to claim 1, wherein each ofthe first region and the second region includes polycrystal having aperovskite structure including barium and titanium.